MOSFETs (Metal Oxide Semiconductor Field-Effect Transistors), can be classified into two types, namely, "analog" and "digital." The two types perform different functions. The digital type acts as a switch: it is either ON or OFF. The analog type acts as an amplifier: it amplifies a signal.
These two types are constructed differently: Analog transistors should have long channels with large surface area. Digital transistors should have channels as short as possible. However, since a short channel produces a large electric field along the channel's length (ie, between the source and the drain), the channel should be sufficiently long that the electric field does not exceed the breakdown value of the channel material. These differences will be explained in more detail.